With the rapid development of semiconductor manufacturing technology, the size of semiconductor devices in an integrated circuit (IC), especially the Metal-Oxide-Semiconductor (MOS) devices, has become smaller and smaller to match the integration and miniaturization requirements of the IC development. Transistors are the major components of MOS devices.
When the size of the transistor is continuously reduced, the gate dielectric layer made of silicon oxide or silicon oxynitride is unable to match the performance requirements. For example, the transistor having the gate dielectric layer made of silicon oxide or silicon oxynitride may have leakage current issue, and/or dopant diffusion issue, etc. Thus, the threshold voltage of the transistor may be adversely affected; and the reliability and stability of the transistor may be reduced.
In order to solve the previously described problems, transistors having a high dielectric constant (high-K) dielectric layer and a metal gate layer have been developed. Such transistors are referred as High-K-metal gate (HKMG) transistors. The HKMG transistors use high-K material to substitute the conventional silicon oxide or silicon oxyinitride as the gate dielectric material; and use metal material or metal compound to substitute the conventional polysilicon as the gate material to form metal gates. The HKMG transistors are able to reduce leakage current, and reduce working voltage and power consumption when the size of the transistors is reduced. Thus, the performance of the transistors may be enhanced.
However, when the technical node of the semiconductor technology is continuously reduced, the size of the HKMG transistors is also continuously reduced; and the device density is continuously increased. Thus, it may be difficult to control the fabrication process of the HKMG transistors; and the performance of the HKMG transistors may be unstable. The disclosed device structures and methods are directed to at least partially solve one or more problems set forth above and other problems.